Lithium-ion secondary batteries have been produced in small capacity, light weight, and large capacity, and widely used as power sources of mobile phones since the advent of 1991.
In recent years, with rapid development of electronic, communication, and computer industries, there have been emerged camcorders, mobile phones, laptop PCs, and so on, now remarkably expanding over again. As power sources for driving those portable electronic information and communication machines, lithium-ion secondary batteries are increasingly demanded from data to day. A small lithium-ion secondary battery, which is currently come into the market, uses LiCoO2 for anode and carbon for cathode.
As anode materials sprightly studied nowadays, there may be LiNiO2, LiCoxNi1-xO2, and LiMn2O4. LiCoO2 is an excellent material having stable charging/discharging characteristics and plane discharge voltage characteristics, whereas there is a need of developing other anode materials because Co is insufficient in deposit, expensive and poisonous to a human body. LiNiO2 is still not commercialized due to bad thermal stability as well as difficulty in synthesizing materials, while LiMn2O4 is partially commercialized for low price products. Otherwise, LiMn2O4 with a spinel structure has a logical capacity about 148 mAh/g which is smaller than that of other material, is smaller than LiCoO2 and LiNiO2, which are structured in second dimension, in diffusion coefficient as diffusion resistance becomes larger when lithium ions are inserted or separated because it has a three-dimensional tunnel structure, and is bad in cycle characteristics due to Jahn-Teller effect. Especially, the high temperature characteristics (in need of description) at 55° C. is inferior to that of LiCoO2 and thus LiMn2O4 is not widely used for a practical battery.
To overcome those demerits, there are proposed methods of preparing lithium secondary battery active materials with high density and uniform particle sizes using co-precipitation, and studies for nickel-manganese-cobalt mixed lithium secondary batteries with low prices.
However, in the case of preparing a nickel-manganese-cobalt composite oxide through co-precipitation, if an amount of nickel increases, there are problems of degrading particle density among primary particles at the initial seed formation and decreasing tap density as a result.